FusionImages: Use ImageMagick for thumbnail generation

[amotl]

These improvements try to address the problems described in #24 regarding conversion of TIFF images with G4 compression.

[amotl]

@Patent2net:

There should be ImageMagick binaries for Windows available.

After that, we will have to tune p2n.util.find_convert to make it work on Windows. Can we humbly ask you to try this by switching to the "fix-thumbnails" branch and then running the "p2n images" (or FusionImages.py directly) command after a "python setup.py {develop,install}"?

Thanks in advance for your efforts!

[amotl]

We can also think about using the scandir module to scan $PATH for all instances of convert and convert.exe to make find_convert() more convenient.

There might eventually be a module on PyPI for doing exactly this, let's check these:

• https://pypi.python.org/pypi/where
• https://pypi.python.org/pypi/which

@Patent2net could you check if this would also yield a good output on Windows after installing ImageMagick? What is your output on Windows, actually?

pip install where
python
>>> import where
>>> where.first("convert")
'/opt/local/bin/convert'

Thanks again!

[amotl]

Dear David,

thanks for merging! However, it was a little bit early as i have considered the amendments as a work in progress yet. I hope it didn't make things worse by breaking the existing functionality.

In any way, i just wanted to tell you that i am just working on appropriate updates to this specific feature as discussed and will add them to this PR soon.

With kind regards, Andreas.